1. Field of the Invention
The present invention relates to motor vehicles and in particular to a method for controlling a turbocharger.
2. Description of Related Art
Methods for manually controlling a turbocharger have been previously disclosed. Johnson (U.S. Pat. No. 6,830,121) is directed to a control system for increasing the fuel economy in a combustion engine by controlling the limit of turbo boost under a given set of conditions related to vehicle speed. Johnson teaches a system where the boost pressure limit (BPL) may be switched on and off with a first switch, and the boost pressure limit value may be adjusted using a second switch. Although Johnson teaches a boost pressure limit, or boost pressure maximum, Johnson fails to teach a system where the user may set a boost pressure minimum or a fixed boost pressure value.
Kanawyer (U.S. Pat. No. 4,598,549) is directed to a turbocharger manifold pressure control system. Kanawyer teaches a turbocharger system including a two position switch where the user selects between a low boost pressure maximum and a high boost pressure maximum. By selecting the low position of the switch, the turbocharged system is configured so that the boost pressure will never exceed the low boost pressure maximum. This may be useful in situations where the user wants to conserve gas or generally maintain low boost pressures within the turbocharged system. By selecting the high position of the switch, the turbocharged system is configured so that the boost pressure will never exceed the high boost pressure maximum. This high switch setting allows the user to make full use of high boost pressures that can be achieved using the turbocharged system.
Kanawyer does not teach the use of multiple switch settings (low, high and intermediate, for example), Kanawyer only teaches the use of a low or high maximum boost pressure setting. Kanawyer also fails to teach the concept of manually selecting a minimum boost pressure.
Jiewertz (U.S. Pat. No. 5,214,919) is directed to an arrangement for regulating the response of an internal combustion engine with a turbocharger. Jiewertz teaches a manual control setting that allows the user to adjust the maximum boost pressure. This is done in order to reduce the jerkiness of the vehicle due to sudden changes in torque that may occur in a turbocharged engine where the boost pressure is allowed to vary dramatically.
Jiewertz discusses two specific manually selected boost pressure settings, a “sporty” mode and a “soft” mode. In the sporty mode, the maximum boost pressure is always available under any load condition of the engine. While this mode provides immediate throttle response, the engine can feel “jerky” to inexperienced drivers. In the soft mode, the maximum boost pressure may be fixed at a lower value for small throttle angles (small engine loads) and at an intermediate value for medium throttle angles (moderate engine loads). By limiting boost pressure at low engine loads, this arrangement helps to improve smoothness under low engine loads. As the engine load increases (represented by increased throttle angle), the soft mode setting is gradually over-ridden, and additional boost pressure is available at greater throttle angles.
Jiewertz does not teach the use of manually selected minimum boost pressures. Additionally, Jiewertz does not teach the use of manually selected ranges for boost pressure. Also, although Jiewertz does teach a manual control setting for adjusting the maximum boost pressure, this value is not constant and is designed to be over-ridden under increasing engine loads, represented by throttle angle. Therefore, the user cannot manually adjust the maximum boost pressure to a value determined by the user. Also, Jiewertz does not teach or suggest the concept of forcing a turbocharger to maintain a minimum boost pressure.
There is a need in the art for a system and method that addresses the problems of the prior art.